Ferrite loopstick antenna arrays for loran c receiver

ABSTRACT

The traditional whip antenna of a loran-C receiver is replaced by an antenna of one or preferably two ferrite loopstick arrays. Each array includes several identical loopsticks, each of which support equal left-hand and right-hand coils connected in parallel. The parallel-connected left-hand and right-hand coils of the loopsticks of each array are connected in series. In each array, the loopsticks are supported with their axes parallel and coplanar and with their ends in-line. The loopstick axes of each array are horizontal and one above the other when the receiver is in use. The arrays are spaced a short distance, are at an angle to each other laterally and are independently adjustable in azimuth for directivity. Each array has an effective height greater than that of the whip antenna it replaces.

Unite States Patent [191 lkrath FERRITE LOOPSTICK ANTENNA ARRAYS FOR LORAN-C RECEIVER Inventor: Kurt lkrath, 232 Lockwood Ave.,

Elberon, NJ. 07740 [22] Filed: June 12, 1973 [211 App]. No.: 369,326

[52] U.S. C1 343/748, 343/103, 343/788 [51] Int. Cl. HOlq 7/08 [58] Field of Search 343/103, 788, 748

[5 6] References Cited UNITED STATES PATENTS 2.951.201 8/1960 Sander 343/103 3,440,542 4/1969 7 Gautney... 343/788 3,495,264 2/1970 Spears 343/788 3.623.116 11/1971 Green et a1. 343/788 3,718,932 2/1973 lkrath et a1. 343/788 Primary Iaimmirwr-13li Lieberman Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; Arthur L. Bowers [57] ABSTRACT The traditional whip antenna of a loran-C receiver is replaced by an antenna of one or preferably two ferrite loopstick arrays. Each array includes several identical loopsticks, each of which support equal left-hand and right-hand coils connected in parallel. Theparallel-connected left-hand and right-hand coils of the loopsticks of each array are connected in series. In each array, the loopsticks are supported with their axes parallel and coplanar and with their ends in-line. The loopstick axes of each array are horizontal and one above the other when the receiver is in use. The arrays are spaced at short distance, are at an angle to each other laterally and are independently adjustable in azimuth for directivity. Each array hasan effective height greater than that of the whip antenna it replaces.

3 Claims, 4 Drawing Figures l \l\\\\\\ V PATENTEDJUN28 1914 3,821 743 SHEET 2 [1F 2 I8 FIG. 2 [6 W \\K\\\\\\///////// V /////////1 A 1 p24 I LORAN-C RECEIVER FIG. 4

LORAN-C RECEIVER FERRITE LOOPSTICK ANTENNA ARRAYS FOR LORAN-C RECEIVER BACKGROUND OF THE INVENTION This invention concerns loran-C. Information on loran and loran-C is in the literature. Volume 4 of the Radiation Laboratory Series published by McGraw-Hill in 1948 is entitled Loran and includes historical background, technology and operational characteristics of loran. Updated information on loran and more particularly loran-C has been published over the intervening years. For example, the book Avionics Navigation Systems, by Kayton and Fried, published by John Wiley and Sons, 1969, includes an updated summary of loran- C on pages 192 through 196. The loran-C receiver has been equipped traditionally with a whip antenna about 3-4 meters long; the more recent loran-C receiver has been equipped also with a digital display for providing a time difference readout. When signal-to-noise ratio is sufficiently poor, the digital display does not stop or sync and it is impossible to obtain a reading.

Loran is a hyperbolic type of radio navigational aid that employs pairs of pulse transmitter stations. Of each pair, one is a master and the other slaved to it in that its pulse transmission is delayed relative to that of the master. Time difference between intercepted signals from a master and slave pair is presented on the digital display of the receiver. A navigational fix is determined from a chart after obtaining time differences for two station pairs. Standard loran operates at a carrier frequency of 1,850KH2 or 1,900KHZ or 1,950KHz. Loran-C has some advantages and some disadvantages over standard loran. Loran-C operates at a carrier frequency of IOOKHz and employs receivers that are smaller, lighter weight, and portable. However, it is a ground wave radio navigation system and the sensitivity of a ground wave radio navigation system when used over land is influenced by weather and by seasons. For example, system sensitivity changes with seasonal changes in ground conductivity caused by rain, snow, and frost and vegetation changes. Receiver sensitivity over land is influenced by terrain characteristics in its vicinity because electric field polarization of ground wave propagated signals locally at the receiver may range from near vertical to forward tilted in varying degree in the direction of propagation linear and elliptical polarization. Also, mountains, boundaries between land and water, and other terrain discontinuities, that present discontinuities in surface electrical impedance effect polarization of the electric field of a ground wave propagated electrical signal. Receiver sensitivity is degraded because the whip antenna senses only the component of electric field parallel to it and the receiver includes no means for determining whether the antenna is in line with the electric field. More particularly, when the digital display does not sync, the receiver conveys no information to the operator which is helpful for aligning the antenna with the electric field so that he cannot take advantage of a temporary improvement in signal strength or signal-to-noise ratio that might sync the digital display. The weather and seasonal factors are less severe in loran-C than in standard loran. The advantages of loran-C over standard loran are offset in varying degree by the presence of a higher level of electrical noise in the lower part of the radio wave spectrum and by the need for physically larger antennas than standard loran. The local noise sensed by a loran-C receiver includes atmospheric noise, man-made radio frequency interference, and quasi-static type tribo electric noise.

Loran-C receivers can be useful on helicopters flying low over unfamiliar terrain, on automotive vehicles and trucks particularly military vehicles operating in unfamiliar territory and also can be useful as manpacks. However engine-produced electrical disturbance and tribo electric noise in the vicinity of a large number of moving vehicles can render useless a whip-antennaequipped loran-C receiver. Manpack receiver usefulness may be limited by the same noise. In the vicinity of modern structures, there is substantial electrical noise that limits the usefulness of such receivers.

SUMMARY OF THE INVENTION An object of this invention is to reduce the abovedescribed handicaps of loran-C receivers and to generally increase their usefulness.

This invention concerns providing a ferrite loopstick antenna array for a loranC receiver to replace the whip antenna. In the frequency range of about IOOKHz, the above ground magnetic field polarization is parallel to the surface. Terrain effects on magnetic field orientation is very much less than on electric field orientation. Where terrain approaches a perfect conductor (seawater with 45mho/m approaches a perfect conductor) electric field polarization is essentially normal to the interface. However, land is a lossy dielectric and electric field polarization tilt angle varies greatly over land in contradistinction to the essentially constant horizontal orientation of magnetic field polarization over land. The ferrite rod loopstick has high signalto-noise ratio and directivity, plus the additional advantage of being relatively insensitive to terrain effects. However, in reasonable length, it does not have adequate effective height for low strength signals. This invention concerns a novel compact planar array of several parallel loopsticks that has signal sensitivity that is superior to that of the whip antenna. The array includes a plurality of coplanar series-connected loopsticks supported with their axes horizontal and in a vertical plane and adjustable in azimuth. Two arrays are used for receiving selected pairs of loran-C stations in a weak signal area by orienting one array to receive the weakest station. Usefulness of loran-C receivers are greatly extended by this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. ll shows a ferrite loopstick antenna array in accordance with this invention wherein the axes of the loopstick are coplanar and parallel;

FIG. 2 is an abbreviated electrical diagram of the antenna array of FIG. 1 showing three of the loopsticks electrically connected in series;

FIG. 3 shows the antenna assembly of FIG. 1, on a much smaller scale than in FIG. I, mounted with the loopstick axes horizontal, arcuately adjustable about a vertical axis and connected to the input of a loran-C receiver; and

FIG. 4 shows a preferred embodiment of this invention wherein two antenna assemblies as in FIG. 1 are connected in parallel to the input of a loran-C receiver and each is supported for independent arcuate adjustment about respective vertical axes.

In FIG. I there is shown seven essentially identical ferrite loopsticks 12 supported with their axes coplanar, parallel and equally spaced, by a nonmagnetic support frame 14. Each ferrite loopstick includes a lefthand wound coil 16 and a right-hand wound coil 18 as is conventional for reduced capacitance effects; leg ends L and R indicate the coils are oppositely wound. Coil I6 and coil 18 of each loopstick are connected in parallel. All of the loopsticks in the array shown in FIG. 1 are connected in series as exemplified by the three loopsticks shown in FIG. 2. The array 14 has terminals 22 and 24. While the array shown has seven loopsticks, this is not intended as a limitation. It may have fewer or more than seven. An embodiment that was made and operated successfully had seven loopsticks and performed with an effective height about three times that of the whip antenna it replaced.

In FIG. 3, antenna assembly 14 is shown mounted on a support 26 and oriented for reception; the axes of the loopsticks are horizontal and above one another. The support and the array are designed to permit azimuthal adjustment of the plane of the array and for clamping the array 14 in the selected azimuthal orientation. Whether the provision for arcuate adjustment is at the lower or upper end of support 26 or at the array 14 rather than as shown in FIG. 3 is not material to performance but does influence compactness and ease of adjustment. FIG. 3 shows transverse member 28 arcuately adjustable on the upper end of support 26 and having a clamp 30 for locking the transverse member 28 to the support 26.

A tuning capacitor 32 is connected across the connecting leads 22, 24 of the array to set the array and tuning capacitor combination for resonance at lOOKl-Iz.

The parallel-connected array 14 and tuning capacitor 32 are coupled to the input of loran-C receiver 34 by coupling capacitor 36 and conductor means 38. The loran-C receiver is equipped with station-pair selection means, not shown. Also, recent loran-C receivers are equipped with illuminated digital display readouts. The array is adjusted in azimuth if a selected station pair does not provide a readout. The embodiment shown in FIG. 4 differs from the one shown in FIG. 3 in that it includes two arrays askew to one another so that a readout for each station pair may be obtained without adjustment of antenna assembly 14. However, each array includes releasable clamping means 40 for arcuate adjustment relative to support 26a. The closest spacing between the arrays should be at least large enough for the arrays to clear each other if oriented in line or coplanar. If signals from a selected station pair cannot be processed by the receiver, one of the arrays or in the alternative, the entire assembly is adjusted in azimuth to obtain a readout from that station pair. Retuning may be required after orientation adjustment. Generally, there will be no problem obtaining a readout from the other station pair.

Commercial size ferrite rods with conventional winding designs on the rods may be used in this invention. The number of loopsticks in'an array as well as the spacings between loopsticks of an array constitute a compromise between size and weight on the one hand and signal sensitivity on the other hand. The relationship between spacing and sensitivity for an array of a selected number of loopsticks may be ascertained empirically.

A mathematical treatment of an antenna according to this invention was prepared by the inventor and published as Research and Development Technical Report, ECOM-3574 of the US Army Electronics Command, Fort Monmouth, New Jersey entitled Ferrite Rod Antenna Arrays for Loran-C Receivers. On its cover it bears the date May 1972; this is not the publication date since the manuscript did not leave the in-house editing office for the printer until June 28, 1972.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In combination, a loran-C receiver, a ferrite loopstick array antenna including a plurality of loopsticks connected in electrical series, the loopstick axes being coplanar and in parallel and the loopsticks being spaced from each other, a tuning capacitor coupled to the array and in combination with the array being tunable to KHZ, means coupling the array and tuning capacitor to said loran-C receiver, and means for supporting the antenna with the loopstick axes horizontal and with the plane of the loopstick axes vertical during signal reception.

2. The combination defined in claim 1 wherein the array antenna includes seven loopsticks that are essentially identical and are equally spaced.

3. The combination defined in claim 1 further comprising a second ferrite loopstick array antenna substantially identical to the first-recited loopstick antenna array and connected in electrical parallel therewith, said means supporting both arrays, the loopstick axes of both arrays being horizontal and the planes defined by both arrays being vertical, said means and each array including arcuate adjustment means for adjusting the respective arrays independently in azimuth. 

1. In combination, a loran-C receiver, a ferrite loopstick array antenna including a plurality of loopsticks connected in electrical series, the loopstick axes being coplanar and in parallel and the loopsticks being spaced from each other, a tuning capacitor coupled to the array and in combination with the array being tunable to 100 KHz, means coupling the array and tuning capacitor to said loran-C receiver, and means for supporting the antenna with the loopstick axes horizontal and with the plane of the loopstick axes vertical during signal reception.
 2. The combination defined in claim 1 wherein the array antenna includes seven loopsticks that are essentially identical and are equally spaced.
 3. The combination defined in claim 1 further comprising a second ferrite loopstick array antenna substantially identical to the first-recited loopstick antenna array and connected in electrical parallel therewith, said means supporting both arrays, the loopstick axes of both arrays being horizontal and the planes defined by both arrays being vertical, said means and each array including arcuate adjustment means for adjusting the respective arrays independently in azimuth. 